The objective of the proposed research is to determine the relationship between chromosome structure and such chromosome functions as the determination of fates of cells during development and the regulation of gene expression. The approach will be to isolate a specific region of a chromosome from types of cells in which its functional state differs and then to compare the composition and structure of the purified materials. Methods will be developed for the fractionation of regions of chromosomes on the basis of solubility, size, DNA sequence, and density. The methods will be applied initially to ribosomal RNA gene and histone gene regions of Drosophila and sea urchin chromosomes. A major goal will be the preparation of crystals or paracrystals of the purified material.